1. Field of the Invention
The invention relates to hydroprocessing hydrocarbonaceous feeds in consecutive upflow and downflow reaction stages, with noncatalytic removal of impurities from the upflow stage vapor effluent. More particularly, the invention relates to a process for removing impurities from a hydrocarbonaceous feed, by catalytically hydroprocessing the feed in a cocurrent upflow first reaction stage, followed by a downflow reaction stage, with impurities removed from the upflow reaction stage vapor effluent, by contacting it with a hydrocarbonaceous liquid. Feed impurities, such as heteroatom (e.g., sulfur) compounds, present in the upflow reaction stage vapor effluent, are transferred to the hydrocarbonaceous liquid by the contacting. The contacting liquid is then combined with the upflow stage liquid effluent and hydroprocessed in the second stage. The impurity-reduced vapor is cooled to condense and recover additional product liquid.
2. Background of the Invention
As supplies of lighter and cleaner feeds dwindle, the petroleum industry will need to rely more heavily on relatively high boiling feeds derived from such materials as coal, tar sands, shale oil, and heavy crudes, all of which typically contain significantly more undesirable components, especially from an environmental point of view. These components include halides, metals, unsaturates and heteroatoms such as sulfur, nitrogen, and oxygen. Furthermore, due to environmental concerns, specifications for fuels, lubricants, and chemical products, with respect to such undesirable components, are continually becoming tighter. Consequently, such feeds and product streams require more upgrading in order to reduce the content of such undesirable components and this increases the cost of the finished products.
In a hydroprocessing process, at least a portion of the heteroatom compounds are removed, the molecular structure of the feed is changed, or both occur by reacting the feed with hydrogen in the presence of a suitable hydroprocessing catalyst. Hydroprocessing includes hydrogenation, hydrocracking, hydrotreating, hydroisomerization and hydrodewaxing, and therefore plays an important role in upgrading petroleum streams to meet more stringent quality requirements. For example, there is an increasing demand for improved heteroatom removal, aromatic saturation and boiling point reduction. In order to achieve these goals more economically, various process configurations have been developed using primarily downflow or trickle bed reactors, including the use of multiple hydroprocessing stages as is disclosed, for example, in U.S. Pat. Nos. 5,522,983; 5,705,052 and 5,720,872. Downflow trickle bed reactors must be designed with a high liquid mass velocity (liquid flow per cross-sectional area) to achieve good contacting of the catalyst with the liquid. This requires the cross-sectional area of the reactor to be small and therefore limited as to the amount of catalyst that it can hold, without the reactor being prohibitively high (e.g., .gtoreq..about.100 ft.). With an existing trickle bed hydroprocessing unit, in order to enable processing of dirtier feeds, increase the feed capacity, increase the purity of the hydroprocessed product, or all three, additional reaction stages must be added. For example, to achieve ultra clean diesel fuel in a preexisting plant, multiple trickle bed reactors would need to be added in series. In addition to the high cost, such a multiple reactor plant would also be hydraulically limited, due to the high pressure drop of the multiple, tall reactors in series. It would be an improvement to the art if either one or all of the above could be accomplished with the addition of only a single reaction vessel containing no more than one or two additional reaction stages. It would be particularly advantageous if this could be achieved without either the pressure drop or need for a tall reaction vessel, that would be required with the addition of more trickle bed reaction stages.